You shouldn't have any problem fixing that broken stud on the right fork.

After removing the other 3 nuts, you should be able to remove the broken stud with pair of pliers, or vice grips. Perhaps you will need to tap the broken stud with a hammer, or heat it with a torch, but it should come out fairly easily. Some penetrating oil will also help loosen the broken stud.

If you can't find a replacement for the stud, just substitute a metric bolt with the proper length. The stud is size M6x25, and costs $0.56 in the United States; it's part #33 in the following diagram.

If you need to substitute a bolt for the stud, the bolt will need to be shorter, perhaps M6x20 or M6x15. You can replace the bolt with the proper stud when the opportunity presents itself later.